Congo Tetra (Phenacogrammus interruptus)

The Congo Tetra is a larger African schooling tetra with a metallic blue, gold and violet sheen that looks superb in a mature planted aquarium. Scientifically it is Phenacogrammus interruptus, a Congo Basin characin rather than a South American tetra, and it is best kept as a confident group with room to swim.

This is a peaceful community fish, but it is not a tiny nano tetra. Adult males can reach around 8 cm and carry extended fins, so the group needs length, clean water and calm companions. In the right aquarium Congo Tetras are active, elegant and much more impressive than their quiet shop-tank behaviour sometimes suggests.

Why Keep Congo Tetras?

Congo Tetras bring a different look to the usual community tetra group. They are deeper-bodied, more graceful and more reflective than small neon-type fish, and mature males develop flowing dorsal, anal and tail fin extensions. Their colour changes with angle and light: blue through the flanks, yellow-gold along the back, violet and red flashes in the fins, and a silver-green body glow when they turn.

They are especially effective in a planted display because the fish occupy open midwater while plants and wood frame the colour. A dark substrate, shaded edges and moderate lighting usually show them better than a bare bright tank. A settled school will cruise together, break apart to feed, then regroup across the open water.

Tank Size And Layout

Plan around a group, not one fish. Six is the sensible minimum, while eight to ten is better if the aquarium is large enough. A tank of at least 150 litres can work for a modest group, but a 90-120 cm long aquarium gives the fish the swimming space they deserve. Length matters because adult Congo Tetras are active and males display across open water.

Use planting around the back and sides, with an open lane through the middle. Vallisneria, Amazon swords, Cryptocoryne, tall stems, floating plants and branchy wood all suit the look. Do not overfill the centre with hardscape; these fish are at their best when they can move as a school.

Good filtration is important, but the current should not blast them around the tank. Gentle to moderate flow, high oxygen, clean water and regular maintenance are the foundations. Congo Tetras can become nervous in sparse new aquariums, so mature filtration and stable water are worth more than chasing an exact decoration style.

Water Conditions

Petra lists this line with a 24-27 C temperature range, pH 6.0-7.8, hardness up to 20 dGH and an adult size around 8 cm. For long-term colour and condition, aim for stable tropical temperatures, low ammonia and nitrite, and a steady maintenance routine. Soft to moderately hard water is usually ideal, but stability is more important than sudden chemical adjustment.

If your tap water is very hard, avoid swinging the pH with quick fixes. Choose hardy plant and tank mate choices, keep nitrate controlled, and acclimate the group slowly. Congo Tetras are not fragile when settled, but they are much better in mature aquariums than in brand-new tanks.

Feeding

Phenacogrammus interruptus is an omnivore. A good daily base is a quality tropical flake or small slow-sinking pellet, supported with frozen daphnia, brine shrimp, cyclops, bloodworm and similar small foods. The group feeds in midwater, so offer food in a way that does not all sink past them before they have time to eat.

Feed small portions once or twice daily. A varied diet helps males keep good fin condition and brings out stronger colour, but overfeeding quickly harms water quality. In mixed communities, check that shy individuals are eating and that faster surface feeders are not taking everything first.

Tank Mates

Congo Tetras suit peaceful community aquariums with other calm fish of similar or smaller temperament. Good options include peaceful dwarf cichlids, Corydoras, small to medium peaceful barbs, rainbowfish in suitable water, other robust tetras and non-nippy community fish. They also work well as a centrepiece school above bottom dwellers.

Avoid fin-nippers and aggressive cichlids. The long fins on mature males can tempt boisterous fish, and constant chasing will keep the group pale and nervous. Very tiny tank mates may also be intimidated by the size and movement of adults, even though Congo Tetras are not naturally predatory community bullies.

Behaviour And School Size

A lone Congo Tetra, or a pair kept in a short tank, will not show the natural behaviour people expect from the species. In a proper group they are calmer, more colourful and more active. Males may display to each other, but in a larger school that display usually stays ritualised rather than damaging.

Females are generally shorter-finned and less intense in colour. Males are more dramatic once mature, with longer extensions and brighter iridescence. A mixed group gives the best social balance, although exact sex ratios are not always possible at smaller sale sizes.

Size Options

This parent product carries several live Shopify size variants. The smaller 2-3 cm fish are useful when building a young group, while larger 4-5 cm, 5-6 cm and XL options give a faster display effect when available. Larger fish usually show stronger colour sooner, but all sizes need the same basic care: a school, space, stable water and peaceful companions.

Keep the size choice practical. If your aquarium is newly set up, wait until it is mature before adding a larger group. If you already have Congo Tetras, choose a size that will not be overwhelmed by the established fish.

Delivery And Arrival

Congo Tetras are packed for live-fish transport with oxygenated bags, insulation and a specialist UK live-animal courier. The Live Arrival Guarantee applies when the delivery and acclimation instructions are followed. First-time customers can use WELCOME10 at checkout where the current offer is eligible.

After arrival, float the bag to equalise temperature, then acclimate gradually. Keep the lights low for the first few hours and do not feed immediately. Most groups settle better when the aquarium is quiet on the first day.

Who This Fish Suits

Choose Congo Tetras if you want a peaceful, colourful schooling fish for a larger planted community. They are a strong choice for aquarists who can provide a mature tank, open swimming length and a proper group. They are less suitable for nano tanks, rough mixed cichlid communities, fin-nipping tank mates or new aquariums that are still biologically unstable.

Natural Habitat

Congo Tetras come from the Congo River drainage, where shaded margins, roots, leaf litter and slower tributary water create a softer, dimmer environment than many bright shop aquariums. That background explains why they often look best with wood, plants, floating cover and darker decor. They do not need a blackwater tank, but they do appreciate cover and security.

In nature the species feeds opportunistically on small invertebrates, larvae, drifting foods and plant material. In the aquarium that translates into variety, not heavy feeding. A fish that receives only one dry food can survive, but a group given a varied routine usually shows better colour and condition.

Colour, Sexing And Display

Young Congo Tetras may look modest at first. Colour develops with size, diet, confidence and water quality. Mature males are usually the show fish: longer fins, stronger colour and more display behaviour. Females are shorter-finned, rounder through the body and usually less intense, but they help the group behave naturally.

The best colour is normally seen when the fish are not frightened. If the group hides, check tank mate pressure, lighting intensity, group size and whether the tank has enough cover around the edges. A larger group in a longer tank often solves the problem more effectively than adding another product or changing water chemistry suddenly.

Daily Care Routine

A good routine is simple: stable temperature, weekly water changes, sensible feeding and regular observation. Watch the school at feeding time. Healthy Congo Tetras should move confidently, take food in midwater and return to schooling after any brief display. Clamped fins, hanging in corners or sudden skittishness usually points to stress, water quality or unsuitable tank mates.

Keep nitrate under control with water changes and plant growth, and avoid large sudden temperature shifts. If the aquarium is heavily stocked, test water more often. Congo Tetras are forgiving in a mature, well-run community, but they are not a shortcut around maintenance.

Common Mistakes

The most common mistake is keeping too few. A pair or trio may look nervous, chase each other or fade in colour because the social pressure has nowhere to spread. Another common mistake is choosing a tank that is too short. These fish are built for movement; a long aquarium makes a visible difference.

Fin-nipping tank mates are another avoidable problem. Tiger barbs, rough cichlids or very pushy feeders can damage fins and stop the school settling. If you want a colourful peaceful display, build the community around calm species rather than asking Congo Tetras to cope with constant pressure.

How They Compare With Smaller Tetras

Compared with Neon, Cardinal or Ember Tetras, Congo Tetras are larger, more open-water focused and more visually dramatic in adult groups. They are not the right choice for tiny aquascapes, but they are excellent when the aquarium needs a midwater feature fish with movement and colour.

Compared with very active barbs or rainbowfish, they are usually gentler and less frantic. That makes them useful in planted community tanks where the fish should add life without turning the display into a chase scene.

FAQ

How many Congo Tetras should I keep?

Keep at least six, with eight to ten preferred where space allows. The group becomes calmer and more colourful when it can school naturally.

Are Congo Tetras peaceful?

Yes, they are peaceful community fish, but they are active and fairly large for a tetra. Keep them with calm tank mates that will not nip fins or outcompete them heavily at feeding time.

Can Congo Tetras live in a planted aquarium?

Yes. They look excellent in planted tanks with open swimming space, shaded edges and darker substrate. They usually leave healthy plants alone.

How big do Congo Tetras get?

Adult size is around 8 cm, with males looking larger because of their extended fins. Give them more space than you would give smaller community tetras.

Source Notes

This listing was checked against Petra Aqua supplier data for SKU S012, FishBase, Seriously Fish and aquarium-care references for Phenacogrammus interruptus. Care guidance has been written for responsible home aquarium keeping rather than search stuffing.